This invention relates to a method of determining a resistive current and more particularly to a method of determining a corona current in a xerographic charging device.
There are many applications where a load current includes both a resistive current component and a capacitive current component. In some applications it is desirable to measure both the resistive component and the capacitive current component where the resistance, capacitance, or both, are unknown or varying.
One such application is a xerographic charging device driven by an AC power supply. Here the load current is the corona current, which comprises both a resistive component and also a parasitic capacitive component. If the resistive and capacitive current components can be measured without knowledge of the absolute or relative values of either the resistance or capacitance of the load, the information can be used to control the AC power supply to ensure improved corona charging performance.
In one embodiment, a load current comprises a resistive current and a capacitive current. The load is driven by a sinusoidal input signal. The resistive current is determined by forming a first signal that is substantially in-phase with and proportional to the sum of the resistive current and the capacitive current; forming a second signal in-phase with the input signal; forming a third signal opposite in phase to the capacitive current; and processing the first, second and third signals to form a result based on the resistive current.
In a further embodiment, a load current comprises a resistive current and a capacitive current. The load is driven by an input signal. The resistive current is determined by forming a first signal in-phase with and proportional to the sum at all frequencies comprised in the input signal of the resistive current and the capacitive current; forming a second signal in-phase with the input signal; forming a third signal proportional to the capacitive current at all frequencies comprised in the input signal; and processing the first, second and third signals to form a result based on the resistive current.